3.5 a new approach to eaf melted steels mcconway - torres.pdf · 2017. 10. 10. · and two 20-ton...

A New Approach to EAF Melted Steels

Author:

Mauricio Torres – Melt Department Manager

Co-Authors:

Ohannes Mangoyan - Vice President of Manufacturing

Charles Scherrer – Plant Metallurgist

SFSA Technical and Operating Conference, December 2016 of 14

McConway & Torley, LLC

McConway & Torley, LLC (M&T) is a green sand steel foundry located in Pittsburgh, PA. For over 145 years, M&T has been producing railroad castings. As the leading manufacturer of couplers and other railroad castings, M&T produces over 30,000 tons of finished castings per year using an automated green sand Kunkel Wagner system and two 20-ton electric arc furnaces (EAF). M&T boasts full cleaning room and heat treating capabilities. We pride ourselves for recycling scrap steel and converting it to functional castings.

The Need for Change

The current deoxidation practice at M&T consists of adding SiMn to the EAF after blowdown. A considerable percentage of SiMn is sacrificed to kill the steel while the balance of the SiMn acts as an alloying addition. As a result of this practice we incur the following:

• Excessive and inefficient SiMn usage • Non-homogeneous bath temperature • Non-homogeneous bath chemistry • Excessive slag generation / disposal • Inconsistent alloy recovery • Unacceptably high back and leg injuries rates

A continuous improvement team led by Hovig Mangoyan took the initiative to attack this problem and explore various options. The agreed upon direction was to efficiently deoxidize the steel in the EAF and perform the alloying step in the ladle during the tapping process.

Improvement Team Findings

1. Determination of the of the SiMn (Silicon Manganese) loss in the furnace: Substantial data was collected and analyzed. To our surprise, the actual SiMn loss was much higher than initially anticipated. Over 30% of the SiMn was lost as a deoxidizer. Inconsistent and unpredictable deoxidation is the prime source for inconsistent alloy recovery.

2. Non homogeneous bath chemistry and temperature: While EAF’s are recognized to be efficient scrap melters, they are also known for non-homogeneous chemistry and temperature due to the lack of stirring action in the EAF.


3. Method of handling alloy additions: The current practice consists of shoveling SiMn through the slag door. Due the fact that this method is labor intensive, the alloy addition to the EAF by means of shovels is unreliable and inconsistent.

4. Safety findings: Our safety records indicate high incident rate related to heat exposure, back pain, and leg / knee injuries.

CURRENT PRACTICE BLOW DOWN AND ALLOY ADDITIONS

Current Practice Loss of SiMn

Our current practice calls for adding SiMn to the furnace after the blow down (refining) of the heat in order to reduce the active oxygen in the steel and bring the Manganese to the desired level in the steel.

After blow down of the heat, the oxygen levels in the bath are very high, averaging 163 ppm of oxygen, resulting in an oxygen level before tap of 30.1 ppm after addition of SiMn. Bringing the oxygen level in the steel to equilibrium with the SiMn results in a loss of the alloy and the formation of SiO2 and MnO which will float and become part of slag.


Improving the Process

It is clear that the excessive free oxygen after blowdown is the root cause of the low SiMn recovery. Naturally, we had to search for a substitute deoxidizer with higher affinity for oxygen than Manganese. The Ellingham Diagram offered the answer to our question. We determined that aluminum was the most economical and practical deoxidizer to be used. This solution however presented a new challenge: due to the low specic gravity and melting temperature of aluminum, it would be challenging to add aluminum through the slag and into the steel. We concluded that a more dense form of aluminum had to be explored. As another option, an alternate method of introducing aluminum in the bath had to be found.

1.08 1.11.04 1.07

1.011.12

1.511.61

1.41 1.471.54

1.74

69% 66% 67% 69% 62% 63%0.5

0.7

0.9

1.1

1.3

1.5

1.7

1.9

900lbs 960lbs 840lbs 880lbs 920lbs 1040lbs

%

Mn

Content

Silico- ManganeseAdded(lbs.)

CurrentPracticeManganeseRecovery

%FinalMn

%MnAdded

%MnRecovery

66%Avg.Recovery


ChangesToTheMeltingStepsCURRENTPRACTICE:

ChargeEAF

Melt RefiningO2Blowdown

AlloyAddition

Tapping/

Deoxidation

LadleFurnace

NEWPRACTICE:

Furnace

ChargeEAF

MeltRefining

O2Blowdown Deoxidation Tapping/

Alloying

Ladle

Ferro-Aluminum (composition: 30% Aluminum 70% Iron)

Initially, we opted to experiment with the addition of Ferro-Aluminum pigs due to the higher specic gravity and melting temperature. Test results were very encouraging in terms of final oxygen levels, reduced SiMn addition levels, and considerably higher SiMn recoveries. In comparison to our current practice, it was easy for the operator to add the FeAl to the furnace. Oxygen levels as low as 3.1ppm were achieved prior to tapping. With this practice it is highly recommended to stir argon gas into the bath to achieve a homogeneous chemistry and temperature. Despite the favorable results, this option was not economical due to the high cost of FeAl compared to that of aluminum.


Ferro-Aluminum Addition and Manganese Recovery

HEAT #1 HEAT #2 HEAT #3 HEAT #4 HEAT #5 HEAT #6 Total lbs.

FeAl 240 205 238 250 226 236

Deoxidation lbs. FeAl

200 205 200 200 200 200

Al lbs. 5 7.5 10 12 12 10 Prelim Mn 0.09 0.04 0.04 0.06 0.03 0.07 SiMn lbs. 740 740 740 700 740 700 ElMn lbs. 0 0 0 0 0 0

Theoretical Mn

1.24 1.24 1.24 1.17 1.24 1.17

Final Mn 1.23 1.01 1.13 1.05 1.09 1.06 Recovery % 92 78 90 85 91 85 Carbon(C) 0.26 0.26 0.28 0.25 0.27 0.25

Manganese (Mn)

1.23 1.01 1.13 1.05 1.09 1.06

Silicon (Si) 0.43 0.41 0.45 0.42 0.47 0.43 Chrome (Cr) 0.55 0.55 0.42 0.45 0.45 0.51 Nickle (Ni) 0.48 0.59 0.42 0.41 0.43 0.52 Moly (Mo) 0.2 0.2 0.17 0.14 0.16 0.16 Aluminum

(Al) 0.055 0.017 0.022 0.018 0.05 0.052

Phosphorus (P)

0.021 0.023 0.028 0.022 0.023 0.018

Sulfur (S) 0.016 0.017 0.018 0.016 0.018 0.019

1.33 1.28 1.281.23

1.271.24

1.23

1.01

1.131.05 1.09 1.06

80%76%

85% 80%84%

80%

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Heat#1 Heat#2 Heat#3 Heat#4 Heat#5 Heat#6

Silico-ManganeseAdded(lbs.)

Ferro-Aluminum

%TheoreticalMn

%FinalMn

%MnRecovery

740lbs740lbs 700lbs740lbs 740lbs 700lbs

80.83%Avg.Recovery

ManganeseRecoveryUsingFerro-Aluminum


Aluminum Plunge (composition: 100% 10 lb. Notch Bar Aluminum)

In our second experiment, we plunged aluminum bars thru the slag into the steel bath. The test data showed similar encouraging low oxygen levels and good Mn recoveries. In this trial, we plunged two-30 lb. aluminum bars. We also ran argon to stir the bath during the addition of the aluminum; as a result we had a very uniform chemistry with a tremendously lower level of oxygen (3ppm). This practice was equally successful and more economical; however, this solution was deemed impractical due to the fact that it is dependent on employee skill besides the fact that it is physically demanding.

PLUNGE DEVICE


Aluminum Bar Plunging vs. Recovery of Manganese

HEAT #1 HEAT #2 HEAT #3 HEAT #4 HEAT #5 HEAT #6 Totallbs.Al 82 82 83 82 82 82

Allbs.Deoxidation

60 60 60 60 60 60

AlLadlelbs. 22 22 23 22 22 22PrelimMn 0.05 0.04 0.08 0.09 0.09 0.05SiMnlbs. 690 690 690 690 690 690ElMnlbs. 0 0 0 0 0 0Theoretical

Mn1.21 1.2 1.24 1.25 1.25 1.21

FinalMn 1.01 1.03 1.11 1.06 1.06 1.07Recovery% 79 82.50 83 78 78 84Carbon (C) 0.28 0.28 0.27 0.28 0.29 0.26Manganese

(Mn) 1.02 1.03 1.11 1.06 1.06 1.07

Silicon (Si) 0.41 0.4 0.43 0.42 0.43 0.41Chrome (Cr) 0.55 0.45 0.45 0.44 0.43 0.45Nickle (Ni) 0.62 0.54 0.51 0.42 0.43 0.47Moly (Mo) 0.15 0.13 0.15 0.14 0.026 0.15Aluminum

(Al) 0.031 0.038 0.029 0.019 0.022 0.042

Phosphorus (P)

0.019 0.021 0.022 0.022 0.018 0.023

Sulfur (S) 0.013 0.017 0.017 0.019 0.019 0.019

1.21 1.2 1.24 1.25 1.25 1.21

1.01 1.031.11 1.06 1.06 1.07

79% 83% 83% 78% 78% 84%

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Heat#1 Heat#2 Heat#3 Heat#4 Heat#5 Heat#6Additionof690lbs.ofSilico-Manganese

AluminumBarAdditionvs.ManganeseRecovery

%TheoreticalMn

%FinalMn

%MnRecovery

80.83%Avg.Recovery

ManganeseRecoveryPlungingAluminumBars


Aluminum Wire Injection (composition: 100% Aluminum)

Our final experiment, consisted of introducing aluminum into the bath by feeding 100% aluminum wire into the bath using a standard wire feed machine. Simultaneously, we stirred the bath with an argon lance. In this case, the recovery of Mn was the highest with minimal employee input.

Aluminum Wire Addition vs. Manganese Recovery

1.2 1.21 1.22 1.221.17

1.13

1.11.13

1.07 1.071.03 1.01

86% 89%83% 83% 84%

86%

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

HEAT#1 HEAT#2 HEAT#3 HEAT#4 HEAT#5 HEAT#6

%

Mn

Content

Silico-ManganeseAdded(lbs.)

AluminumWireInjection

%TheoreticalMn

%FinalMn

%Recovery

670lbs.690lbs. 690lbs. 690lbs. 690lbs.

650lbs.

85.16%Avg.Recovery


HEAT #1 HEAT #2 HEAT #3 HEAT #4 HEAT #5 HEAT #6 Totallbs.Al

Wire68 68 68 68 68 68

Allbs. 14 12 12 0 12 12Prelim#2

Mn0.04 0.05 0.06 0.06 0.07 0.05

SiMnlbs. 690 690 690 690 670 670Theoretical

Mn1.2 1.21 1.22 1.22 1.19 1.17

FinalMn 1.1 1.13 1.07 1.07 1 1.03Recovery% 95 97 92 92 89 92Carbon (C) 0.26 0.27 0.29 0.26 0.2 0.26Manganese

(Mn) 1.1 1.13 1.07 1.07 1 1.03

Silicon (Si) 0.45 0.45 0.44 0.41 0.4 0.41Chrome (Cr) 0.48 0.45 0.42 0.51 0.5 0.48Nickle (Ni) 0.54 0.5 0.54 0.52 0.49 0.52Moly (Mo) 0.17 0.14 0.14 016 0.14 0.13Aluminum

(Al) 0.03 0.05 0.071 0.035 0.024 0.036

Phosphorus (P)

0.022 0.025 0.024 0.025 0.24 0.023

Sulfur (S) 0.014 0.18 0.06 0.019 0.02 0.018Calcium(Ca) 0.0002 0.001 0.0006 0.0003 0.0003 0.0007

Is Aluminum Wire Injection The Way To Go?

As in any new proposed process, we had to validate the process. We compared the following properties:

§ Chemistry § Mechanical Properties § Charpy § Microstructure

ManganeseRecoveryUsingAluminumWire


Average Heat Chemistry for Current Practice vs. New Practice

C % Mn % Si % Cr % Ni % Mo % Al % P % S % AIM .24/.30 .90/1.30 .35/.65 .40/.70 .40/.70 .12/.25 .015 Min .030

Max .030 Max

CURRENT PRACTICE

.27 1.11 .46 .47 .490 .170 .044 .022 .016

NEW PRACTICE

.27 1.07 .42 .47 .510 .150 .045 .023 .020

Average Physical Proprieties of Aluminum Wire Deoxidized Heats

UTS (psi)

YS (psi)

% EL % RA CV ft-lb. @ -40°F

AAR Min. for E-Grade Steel

120,000 100,000 18 30 20

CURRENT PRACTICE

132,000 118,000 17.9 45.6 33.5

NEW PRACTICE

127,000 119,000 18.8 44.7 41.0

Standard Deviation Comparisons of Current Practice vs. New Practice

UTS (psi) YS (psi) % EL % RA CURRENT PRACTICE 6,658 2,482 2,482 6,591

NEW PRACTICE 5,093 1,635 1,635 3,729

Microstructure Comparison

CurrentPractice NewPractice

25.00um 50.00umMagnification:


Discussion and Conclusions

Once an efficient and economically feasible furnace deoxidation has been established, the ladle alloying became possible while offering significant savings due to reduced alloy additions. This practice translates into a 14.5 lbs. /ton of SiMn savings. Two additional pieces of equipment had to be purchased to fully implement the new process.

Silico-Manganese $352,795 Savings Aluminum Cone/Wire $ 35,167+↑ Additional Costs Total Savings per Year $317,628

1) Robot

This piece of equipment will allow us to wire feed aluminum into the furnace and simultaneously bubble argon into the steel to stir the bath. This robot will also measure and record furnace temperatures, perform the oxygen blow down and take chemistry samples for chemical analysis from the bath.

With this piece of equipment we not only improve the deoxidation practice, but we also reduce the heat exposure of the furnace operator. The furnace operator will no longer be required to blow down the heats and take steel samples. The purchase of this equipment will also reduce the amount of man-hours needed to produce a ton of steel. Because argon is needed to stir the bath when aluminum wire is injected; the argon stir will improve the homogeneity of the steel before tap to help achieve a more uniform temperature and chemistry.

AVERAGE ANNUAL SAVINGS


Preliminary Robot Design

2) Alloy Feeder

An Automatic Alloy Feeder is the second piece of equipment required. This machine will allow us to automatically feed the alloy additions to the ladle during tapping. Load cells are incorporated in the machine to weigh the appropriate amount of alloy needed in each heat and also record the amount of usage for inventory purposes.

The alloy feeder will eliminate the handling of one ton of alloy per heat by the operators. This will reduce on safety incidents by eliminating the weighing, staging and shoveling a half ton of alloy into the furnace multiple times a day. This strenuous physical activity was the root cause of many injuries in the last several years.


Final Alloy Feeder Design

3.5 a new approach to eaf melted steels mcconway - torres.pdf · 2017. 10. 10. · and two 20-ton...

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