Spot welded joint

• US 10,081,073 B2
• Filed: 04/25/2013
• Issued: 09/25/2018
• Est. Priority Date: 04/25/2012
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Nippon Steel & Sumitomo Metal Corporation (Nippon Steel Corporation)
• Inventors: Watanabe, Fuminori, Tanaka, Tomohito, Furusako, Seiji, Miyazaki, Yasunobu, Hamatani, Hideki, Oikawa, Hatsuhiko
• Primary Examiner(s): Kwiecinski, Ryan D
• Application Number:
  US14/395,970
• Publication Number:
  US 20150104243A1
• Time in Patent Office: 1,979 Days
• Field of Search: 403270, 403271, 403272
• CPC Class Codes: B23K 11/11 Spot welding
• CPC Class Codes: B23K 11/16 taking account of the properties of the material to be welded
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: H01L 2924/01015 Phosphorus [P]

Abstract

In a spot welded joint according to an aspect of the present invention, with respect to a rectangular planar region of 100 μm×100 μm which is perpendicular to a sheet surface of the plurality of the steel sheets and which centers around an inner point spaced away by 100 μm in a direction parallel with the sheet surface from an edge of a nugget, in a case of measuring a P concentration at a pitch of 1 μm to obtain measured values of the P concentration at 100×100 of measurement points, and in a case of repetitively calculating an average value of the measured values of the P concentration at 20 of the measurement points which are adjacent to each other and which are arranged in a row in the direction parallel with the sheet surface among the 100×100 of the measurement points while shifting each one point to obtain 81×100 of the average values, the number of the average values which are more than two times an average P concentration is 0 to 100.

Claims

1. A method of forming a spot welded joint, comprising:

providing a plurality of overlapping steel sheets containing 0.001% to 0.05% of P; and

forming a nugget in an overlapped face of the plurality of the overlapping steel sheets, wherein the spot welded joint is formed by;

performing a main energizing process with a current value I_w (kA) for energizing time t_w (msec) while applying a welding pressure,

after performing the main energizing process, performing a solidification process by retaining an energizing with a current value I_s (kA) satisfying an Expression (1) for an energizing time t_s (msec) satisfying an Expression (2) while maintaining the welding pressure, and

after performing the solidification process, performing a post energizing process with a current value I_p (kA) satisfying an Expression (3) for an energizing time t_p (msec) satisfying an Expression (4), the energizing time t_p being 60 msec or longer, wherein the Expressions comprise;

0≤

I_s≤

(½

)^1/2×

I_w 

 

(1),

α

²×

{2×

(I_s²/I_w²)+1}×

h≤

t_s≤

3×

α

²×

{2×

(I_s²/I_w²)+1}×

h 

 

(2),

I_p>

0.8×

I_w 

 

(3), and

I_p²×

t_p≤

I_w²×

t_w 

 

(4),

where h is an average sheet thickness in terms of mm of the plurality of the overlapping steel sheets, and a is a nugget diameter (mm)/(h(mm))^1/2.

2. The method according to claim 1, wherein a tensile strength of the plurality of the overlapping steel sheets is 750 MPa to 2500 MPa.

3. The method according to claim 1, wherein a diameter of the nugget in terms of mm is 3×

h^1/2 to 7×

h^1/2.