Method of laser cutting steel

Abstract

A method for laser cutting a steel alloy sheet/plate having a composition including, in wt. %: C: 0.0-0.29; Mn: 0.50-1.35; P: 0.04 max; S: 0.05 max; Si: 0.40 max; Cr: 0.5-0.75, and the remainder being iron and impurities, the steel alloy is free from intentional additions of Cu and Ni and containing less than 0.05% of total cumulated amounts of Cu and Ni.

Claims

1. A method for laser cutting a steel alloy sheet/plate, the method comprising the steps of: providing a steel cutting laser; providing a laser cuttable steel alloy sheet/plate, the steel alloy sheet/plate having a composition consists, in wt. %, of: C: 0.10-0.25; Mn: 0.8-1.2; P: 0.04 max; S: 0.05 max; Si: 0.15 max; Cr: 0.55-0.75, and a remainder being iron and impurities, the steel alloy being free from intentional additions of Cu and Ni and containing less than 0.05% of total cumulated amounts of Cu and Ni; directing a laser beam from the steel cutting laser to the laser cuttable steel alloy sheet/plate; and cutting said laser cuttable steel alloy sheet/plate with the laser beam.

2. The method as recited in claim 1 wherein the steel comprises C: 0.12-0.23.

3. The method as recited in claim 2 wherein the steel comprises Mn: 0.8-1.05.

4. The method as recited in claim 3 wherein the steel comprises Si: 0.02-0.14.

5. The method as recited in claim 4 wherein the steel comprises Cr: 0.55-0.72.

6. The method of claim 1, wherein the steel alloy sheet/plate has a yield strength of at least 250 MPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) One type of mild steel that is often cut by laser is the ASTM A36 type steel for structural applications. The compositional specifications for A36 mild steel plates is, in wt.%: C: 0.29 max; Mn: 0.80-1.20; P: 0.04 max; S: 0.05 max; Si: 0.40 max, (preferred for thicker plates 0.15-0.40). The steel must have a minimum Yield Strength of 250 MPa.

(2) Another type of steel that can be cut by lasers is the ASTM A572 type steel. The compositional specifications for A572 is, in wt. %: C: 0.26 max; Mn: 0.50-1.35; P: 0.04 max; S: 0.05 max; Si: 0.40 max, (preferred for thicker plates 0.15-0.40). The steel must have a minimum Yield Strength of 290 MPa.

(3) The instant invention is a method for laser cutting an improved laser cuttable version of such A36 and A572 steels. The inventive method includes providing a steel cutting laser and providing steel sheet or plate have a broad compositional range of C: 0.01-0.29; Mn: 0.50-1.35; P: 0.04 max; S: 0.05 max; Si: 0.40 max, (preferred for thicker plates Si: 0.15-0.40); Cr: 0.5-0.75; and the remainder being iron and impurities. The method also includes the step of directing a laser beam from the steel cutting to the laser cuttable steel alloy sheet/plate and cutting the laser cuttable steel alloy sheet/plate with the laser beam.

(4) Further the inventive method may provide alloys are free from intentional additions of Cu and Ni. That is, the alloy may contain residual levels of Cu and Ni only, nothing higher. In the inventive method, the steel includes a maximum cumulated amount of Cu and Ni such that (in wt %): Cu+Ni 0.05%. In a preferred embodiment, the maximum cumulated amount of Cu and Ni is below 0.02%.

(5) Preferably the alloys of the present inventive method have a composition in wt. % of: C: 0.10-0.25; Mn: 0.8-1.2; Si: max 0.15; and Cr: 0.55-0.75. Most preferably the alloys of the present inventive method have a composition in wt. % of: C: 0.12-0.23; Mn: 0.8-1.05; Si: 0.02-0.14; and Cr: 0.55-0.72.

(6) Examples of laser cuttable steels useful for the present method are presented in Table 1. The compositions are given in wt. %. Cu and Ni are only present in residual amounts.

(7) TABLE-US-00001 TABLE 1 Heat No C Mn P S Si Cr Ni Cu 1 0.23 1 0.02 0.01 0.03 0.59 0.01 0.01 2 0.19 0.84 0.02 0.01 0.02 0.56 0.02 0.02 3 0.22 1.02 0.01 0.01 0.02 0.57 0.01 0.01 4 0.2 0.86 0.01 0.01 0.02 0.55 0.01 0.01 5 0.12 0.95 0.007 0.005 0.138 0.72 0.02 0.03

(8) Table 2 discloses the composition, in wt. %, of three prior art (commercially available) laser cutting steel comparative samples. As can be seen, the prior art steels have amounts of Cu and Ni added intentionally and significantly lower contents of Cr than the inventive steels.

(9) TABLE-US-00002 TABLE 2 Sample C Mn Si P S Ni Mo Cr Cu C1 0.15 0.95 0.131 0.011 0.006 0.21 0.006 0.09 0.244 C2 0.155 0.788 0.051 0.008 0.005 0.136 0.036 0.048 0.275 C3 0.155 1.166 0.028 0.028 0.004 0.127 0.037 0.107 0.275

(10) Plates of the alloys useful in the inventive method and comparative examples (25.5 mm and 19 mm) were tested for their laser cutting performance. The cutting performance was tested in both the as-hot-rolled condition and the hot-rolled/shot-blasted condition. Hot rolled coils within the compositional range up to 25 mm thick were also tested in the as-rolled, shot blasted and pickled & oiled condition. Laser cut trials indicate that the laser cut quality of inventive steel plates and coils is better than the comparative prior art laser ready steel plates.