# US 4,398,950 A · High strength cold rolled, weldable steel strip

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- Number: US 4,398,950 A
- Document ID: US4398950A
- Status: Granted
- Kind: A
- Application number: 06/056,329
- Filed: 1979-07-10
- Granted: 1983-08-16
- Earliest claimed: 1979-07-10
- Assignees: Inland Steel Company
- Inventors: Indra Gupta; Raymond V. Fostini; Timothy E. Moss
- Web page: https://patentgrep.com/patent/US4398950A

## CPC

- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C21D 8/0236: {Cold rolling}
- C22C 38/14: containing titanium or zirconium
- C21D 8/0273: {Final recrystallisation annealing}
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)

## Abstract

A cold rolled steel strip is provided with a relatively high yield strength together with good resistance spot weldability, while avoiding rolling problems during its manufacture. This is accomplished by adding, to plain carbon steel, phosphorus in an amount greater than 0.04 wt. % up to 0.15 wt. % and 0.04-0.14 wt. % titanium.

## Claims

### Claim 1

A strong, ductile, cold rolled steel strip having good resistance spot weldability, said strip comprising:
a composition consisting essentially of, in wt.%:
______________________________________ carbon .04-.10 manganese .3-.7 silicon 0.01-0.30 aluminum 0.03-0.12 sulfur .03 max. phosphorus greater than .04 up to .15 titanium .04-.14 iron essentially the balance; ______________________________________
and a yield strength in the range of about 40,000-60,000 psi (276-414 MPa).

### Claim 2 (depends on 1)

A cold rolled steel strip as recited in claim 1 and having a ductility, expressed as uniform elongation, of 18-22%.

### Claim 3 (depends on 1)

A cold rolled steel strip as recited in claim 1 and comprising:
a recrystallized grain structure having an ASTM grain size in the range 10-13.

### Claim 4 (depends on 1)

A cold rolled steel strip as recited in claim 1 wherein:
said steel strip has a weldability index expressed as ##EQU2## in the range of about 0.5-1.0.

### Claim 5 (depends on 1)

A cold rolled steel strip as recited in claim 1 wherein:
said steel strip produces weld nuggets, when resistance spot welded, which exhibit a ductile peel test fracture which is substantially insensitive to increased hold time during the welding operation.

### Claim 6 (depends on 1)

A cold rolled steel strip as recited in claim 1 wherein:
said steel strip is weldable over a relatively wide current range comparable to a plain carbon steel strip having the same composition but without alloying additions of phosphorous and titanium.

### Claim 7 (depends on 1)

A cold rolled steel strip as recited in claim 1 wherein:
the ductile to brittle transition temperature for a resistance welded nugget on said strip, subjected to shear impact testing, is in the range -40.degree. to -80.degree. C.

### Claim 8

A method for improving the resistance spot weldability of a cold rolled steel strip having a composition consisting essentially of, in wt.%:
______________________________________ carbon .04-.10 manganese .3-.7 silicon 0.01-0.30 aluminum 0.03-0.12 sulfur .03 max. iron essentially the balance, ______________________________________
while providing said cold rolled steel strip with a yield strength in the range 40,000-60,000 psi (276-414 MPa), said method comprising the step of:
including, in the composition of said cold rolled steel strip, 0.04-0.14 wt.% titanium and greater than 0.04 up to 0.15 wt. % phosphorous.

### Claim 9 (depends on 7)

A method as recited in claim 7 wherein said cold rolled steel strip has a ductility, expressed as uniform elongation, of 18-22%.