w w w . a u t o s t e e l . o r g

BAR APPLICATIONS GROUP

MACHINABILITY SUBCOMMITTEE

Jody Burke

Technical Service Engineer

Gerdau Special Steel North America– Jackson Office

w w w . a u t o s t e e l . o r g

Bar Machinability Committee Members

http://www.autosteel.org/Programs/Bar%20Machinability.aspx

WEBSITE

w w w . a u t o s t e e l . o r g

Bar Applications Group

Machinability Subcommittee

• The goal of the Bar Applications Group (BAG) is to provide

the metalworking industry with pre-competitive information

on which to build their processes in manufacturing

components from steel long products (bars and tubes).

• The Machinability Sub-Committee is one of the sub-

committees under BAG that has:

1. Developed a single-point long turning test for evaluating the

machinability of steel

2. Compiled comparative machinability data on a number of steel

alloys

3. Developed a steel machinability calculator to estimate cutting tool

life based on defined criterion

w w w . a u t o s t e e l . o r g

Bar Machinability Database

The Bar Machinability Sub-committee was formed in 1991 to develop a database of

automotive bar steel machinability under single point carbide turning conditions. To

accomplish this task more than 30 industrially significant steel grades and their

variants have been evaluated in the ensuing years.

w w w . a u t o s t e e l . o r g

Bar Machinability Estimator

The Machinability Estimator was developed for carbon and alloy steels using

uncoated carbide tools. The estimates resulting from this estimator are used only as a

guideline or relative comparison of work-piece materials in selecting materials and/or

machining set-ups and are in no way intended to represent an absolute value.

w w w . a u t o s t e e l . o r g

Machinability Summit Roundtable

Machinability Summit Roundtable Meeting

• Twenty representatives from the industry met on June 26,

2012 at AISI in Southfield, Michigan to discuss the

industry’s needs for steel bar machinability data and the

future role of the Bar Machinability Subcommittee.

• The meeting concluded the following.

– The industry needs to be able to more accurately predict

machinability (Predictability)

– The industry needs to better understand the factors that

contribute to machinability variation (Consistency).

– To be consistent with Subcommittee’s mission, the

initiatives should be data generation and not problem

solving initiatives

w w w . a u t o s t e e l . o r g

Machinability Summit Roundtable

Predictability

• Predictability is driven by the need to accurately predict the

cost of machining as a function of material machinability,

cutting tool life, product through-put, etc.

• Initiatives that fall under “Predictability” and within the

Machinability Subcommittee mission include:

– Modeling

– Developing machinability tests that correlate with actual

machining process results

– Populating material databases that facilitate optimum

steel selection.

w w w . a u t o s t e e l . o r g

Machinability Summit Roundtable

Consistency

• Consistency is driven by the need to minimize unplanned

downtime, which is the largest contributor to machining

cost.

• Initiatives that fall under “Consistency” and within the

Machinability Subcommittee mission include identifying and

quantifying the factors that affect machinability:

– Steelmaking

– Chemistry

– Steel processing / heat treating

– Microstructure

w w w . a u t o s t e e l . o r g

Machinability Summit Roundtable

Conclusion

The Machinability Subcommittee will focus on three initiatives

1. Develop a drilling database

• Drilling is hampered by the lack of an industry standard test, which

tends to discourage evaluation. However, its impact on cycle time,

productivity and cost encourages consideration.

2. Expand the turning database

• The industry acceptance of the single point turning test provides an

incentive to expand the turning database to include:

– Effect of steel processing and chemistry on machinability

– Effects of heat treatment on machinability

– Development of upper and lower machinability limits

– Expansion of database to cover European grades, micro-alloy steels and

stainless steels

3. Technology Transfer

• Outreach initiative to increase awareness of the turning database and

machinability calculator

w w w . a u t o s t e e l . o r g

AISI Bar Steel Fatigue Project

Carbon and Low Alloy Bar

Steels

w w w . a u t o s t e e l . o r g

Project Goals

• Provide Carbon and Low Alloy Steel Fatigue Data for Use in Ground Vehicle Component Design

• Develop a Comprehensive Internet Database to Provide Access to the Fatigue Data

• Provide Information on the Effects of Steel Composition and Processing on Fatigue Behavior

w w w . a u t o s t e e l . o r g

Work Recently

Completed

• Effects of Section Size on Fatigue Properties of

the Core of Carburized Steels

• Comparison of the Fatigue Properties of

Microalloyed Steels as Forgings Versus Hot-

Rolled Bar

• Effects of Sulfur on Fatigue Performance

• Effect of Overloads on Fatigue Performance

• Expansion of the Bar Fatigue Database With

Additional Data

w w w . a u t o s t e e l . o r g

Fatigue Properties of Simulated Carburized

Cores-Effects of Section Size and Hardness

SAE 4320 Steel

15.2mm 38.6 HRC

30.5mm 29.2 HRC

w w w . a u t o s t e e l . o r g

Fatigue Properties of As-Rolled

and Forged Microalloyed Steel

Forged Crankshaft

As-Rolled Bar

1538MV Steel

w w w . a u t o s t e e l . o r g

Long. 0.077%S

Trans. 0.077%S

SAE 4140 Steel 388-395 BHN

Strain-Life Curves-Effect Of Sulfur

w w w . a u t o s t e e l . o r g

0.004%S

0.012%S

0.077%S

SAE 4140 Steel 477 BHN

Tested Transverse to Sulfides

Strain-Life Curves-Effect Of Sulfur

w w w . a u t o s t e e l . o r g

Periodic OverloadTesting Profile

w w w . a u t o s t e e l . o r g

Effect of Overloads on Fatigue Performance

0.01%

0.10%

1.00%

10.00%

1E+2 1E+3 1E+4 1E+5 1E+6 1E+7 1E+8

Tru

e S

train

Am

plitu

de,

De

/2, %

Reversals to Failure, 2Nf

True Strain Amplitude vs. Reversals to Failure

Constant Amplitude Total Strain Amplitude Curve

Overload Data

4140 Steel Q&T 40HRC

Tested Transverse To

MnS Inclusions (0.012%S)

w w w . a u t o s t e e l . o r g

Effect of Sulfur on Overload Fatigue

0.01%

0.10%

1.00%

10.00%

1E+2 1E+3 1E+4 1E+5 1E+6 1E+7 1E+8

Tru

e S

train

Am

plitu

de,

De

/2, %

Reversals to Failure, 2Nf

True Strain Amplitude vs. Reversals to Failure

Constant Amplitude Curves

0.077S

0.012S

0.004S

Overload Data

0.004S 0.012S 0.077S 4140 Q&TSteel 40HRC

Tested Transverse To

MnS Inclusions

w w w . a u t o s t e e l . o r g

Ongoing and Future

Work

• Develop the Fatigue Properties of Case-Carburized

Steels Under Axial Loading

• Development of 4-Point Bending Fatigue Properties

for Case Carburized Steels

• Undertake Rotating Bending Fatigue Studies

w w w . a u t o s t e e l . o r g

North American

Light Vehicle Metallic Material Trends

Great Designs in Steel is Sponsored by:

Use your web-enabled device to download the presentations from today’s event

PRESENTATIONS WILL BE AVAILABLE MAY 3